Barium crown glass



Patented Apr. 28, 1936 UNITED STATES PATENT OFFICE BARIUM CROWN GLASSFrederick Gelstharp, Tarentum, Pa., assignor to Pittsburgh Plate GlassCompany, a corporation of Pennsylvania No Drawing. Application February19, 1934, Serial No. 711,907

Claims. (Cl. 10636.1)

The invention relates to barium crown glass The glass of the foregoingexample has a re-' designed for optical purposes and particularly forciprocal of dispersion of approximately 50, and the production ofbifocal ophthalmic lenses in an index of refraction of 1.616. which thereciprocal of dispersion must be at I am aware that the use of stanniccompounds 5 least approximately 45, together with a high inin glass isnot broadly new, as instanced in Letdex of refraction. The invention hasfor its obters Patent granted to Walter H. Rising N0. jects theprovision of an improved glass of the 1,737,685 and 1,737,686, but insuch cases, the tin character specified which shall be free from deoxidehas been used as a reducing agent and as vitrification orcrystallization, and at the same a colorizer, and in such cases, theglasses are not time shall be resistant to atmospheric attack, bariumcrown glass and the purpose of the tin 10 known in the optical trade astarnish. oxide is entirely foreign to the present invention I have foundthat by using tin in a barium which relates toaspecific improvement inbarium crown batch, the resistance to tarnishing due to crown glass bythe use of a relatively small pert ac on o the atmosphere W be eat yincentage of the tin oxide to increase its resistance 5 creased. Theamount of tin oxide (SnO2) in the to tarnishing without adverselyaffecting the glass finished glass is preferably about 2 per cent, forthe intended use in other respects. No claim but the amount may varyconsiderably, and may is made, therefore, to the use of tin oxide otherbe as low as 1 per cent or as high as 10 per cent. than in theparticular barium crown optical glass Following is an example of a b chW c may described and claimed herein employing the limbe employed: itedquantity of the oxide described and claimed 20 Pounds for the purposeset forth in the specification.

Sand 1 0 What I claim is: Barium carbonate 940 1. A barium crown opticalglass which would Soda ash 192 normally be subject to tarnishingcontaining Calcium carbonate 214 suflicient tin oxide to render theglass resistant to 25 Boric acid 200 tarnishing. Lead oxi-de 172 2. Abarium crown optical glass which would Zinc oxide 4 normally be subjectto tarnishing containing from Sodium nitrate 50 1 per cent to 5 per centof tin oxide.

Antimony oxide 75 3. A barium crown optical glass which would 30 Tinoxide 60 normally be subject to tarnishing containing in excess of 20per cent of barium oxide and 1 to 5 One analysis of the glass producedis as folper cent of tin Oxide.

lows 4. A barium crown optical glass whichwould SiOz 41.09 normally besubject to tarnishing containing from 35 BaO 30.00 1 to 5'per cent oftin oxide and having a recipro- NazO 5-18 cal dispersion in excess of45. CaO 4-83 5. A barium crown glass having a refractive B203 4.65 indexin excess of 1.6 and a reciprocal of disper- PbO 6.78 sion in excess of45, and including a suflicient 0 ZnO 1.93 amount of tin oxide to renderthe glass resistant SbzOa 3.08 to tarnishing.

SnOa 2.46 FREDERICK GELSTHARP.

